The London, Edinburgh and Dublin philosophical magazine and journal of science . t appeared that for the ordi-nary ray polarized in a plane parallel to the line 0 0 1, the indicesof refraction of red light, of the brightest part of the spectrum,and of violet light were about 2*15, 2*159, and 2*314 respectively,and that, for the extraordinary ray polarized in the plane 0 01, Geological Society, 155 the indices of refraction of red light, the brightest part of the spec-trum, and of violet light were about 1*890, 1*973, and 2*143 re-spectively. Carbonate of Thallium. The faces which have been obs
The London, Edinburgh and Dublin philosophical magazine and journal of science . t appeared that for the ordi-nary ray polarized in a plane parallel to the line 0 0 1, the indicesof refraction of red light, of the brightest part of the spectrum,and of violet light were about 2*15, 2*159, and 2*314 respectively,and that, for the extraordinary ray polarized in the plane 0 01, Geological Society, 155 the indices of refraction of red light, the brightest part of the spec-trum, and of violet light were about 1*890, 1*973, and 2*143 re-spectively. Carbonate of Thallium. The faces which have been observed are all in one zone, andexhibit a symmetry which is compatible with either the prismaticor the oblique system. The crystals probably belong to the pris-matic system. They are aggregated in such a manner as to renderit very difficult to isolate a single crystal, or to determine the faceswhich belong to the different individuals of a group of crystals. Observed forms :—1 0 0, 1 I 0, 2 1 0, 1 2 0. Fig. 4. 1 0 0, 1 1 01 0 0, 2 1 010 0, 12 01 1 0, I 1 0 51 2832 768 57 77 4. Twins. Twin face 110. One individual is generally united toeach of two others, in this respect resembling the twins of cerus-site, aragonite, glaserite, and chrysoberyl. A cleavage has been observed probably parallel to the faces of theform 110; it may, however, be parallel to the faces of the form 1 0 0,the complexity of the twin crystals being such that it could notbe ascertained whether the cleavages observed belonged to one crys-tal or to two different crystals. I am indebted to Mr. Crookes, the discoverer of thallium, for thecrystals of nitrate, sulphocyanide, and carbonate of thallium, abovedescribed. GEOLOGICAL SOCIETY. [Continued from vol. xxx. p. 453.] November 22, 1865.—W. J. Hamilton, Esq., President, in the Chair. The following communications were read :— 1. On the impressions of Selenite in the Woolwich Beds andLondon Clay. By P. Martin Duncan, , Sec. Spaces formerly occupied by
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